The weather may not agree, but we're speeding toward summer, and the Major League season is now officially a month old. That's nowhere near enough time to make any really big determinations, but it's at least enough to start forming some impressions.

It's essential not to overreact to seeming trends, and also to be aware of the always-dangerous confirmation bias. Still, we've now seen all 30 rosters in action, and as long as you don't lean too far out over the ledge, perhaps there are some conclusions to be drawn from early-season play.

So with the caveat that all of this could look awfully wrong 31 days from now, here's a glance at five things we seem to have learned from the first month of the 2013 regular season.

We might have underestimated the Red Sox: Boston is hitting, and that wasn't very hard to foresee. Even if the Sox don't have the same kind of superstar-laden lineup from recent years, they have a very deep starting nine, with danger at every position and even off the bench. They're hitting, and they're going to keep hitting.

But it appears that the hiring of manager John Farrell may have accomplished its goal: to help reclaim the careers of Boston's top starting pitchers. Jon Lester, and especially Clay Buchholz, have been excellent, and it's on the pitching arms of those two men that Boston's playoff hopes primarily rest. Ryan Dempster has also been quite good, and Felix Doubront is promising.

Sure, Buchholz won't keep up an ERA in the low 1s all year. But he and Lester have both been Cy Young Award candidates in the not too distant past. They're capable of being front-of-the-rotation starters, and if they are, the Sox will be a load.

We might have overestimated the Blue Jays: Toronto may yet right itself. Brett Lawrie, Melky Cabrera, Colby Rasmus and Jose Bautista may well heat up. The rotation will surely settle in. But it's not just the Blue Jays' record that gives cause for pause. It's the way they're accumulating losses. They're not just having bad luck. It's not the little things they're struggling with; it's the big ones.

The defense has not been sharp. That vaunted lineup is not getting on base -- 14th out of 15 American League teams. They're hitting homers, but with no runners on base, it's not enough to create a good offense. And with Jose Reyes not due back for a good while, that may not get better.

Then there's the rotation, with its own set of concerns. Josh Johnson started slowly and is now dealing with a triceps injury. R.A. Dickey hasn't found his 2012 form, though he hasn't been bad. Mark Buehrle has been very hittable. It's entirely possible the Blue Jays turn this all around, but the caution flags are real.

Bryce Harper might not be human: The Nationals' young slugger is off to a dazzling start. He leads the National League in OPS. He's second in home runs with nine, but he also has the fewest strikeouts of any player with at least seven homers. In short, he's doing it all at the plate: hitting for average, getting on base and hitting for power.

And of course, he's still 20. We should always be careful with paces, but even so, take note of this: Harper is on pace to hit 56 home runs while striking out 100 times. Three players in Major League history have hit at least 30 home runs while striking out 100 or fewer times at age 20 or younger, and they're all in the Hall of Fame: Mel Ott, Frank Robinson and Ted Williams.

It's not that Harper has jaw-dropping tools. We knew that. It's that, at 20 years old, he's already turned those tools into jaw-dropping skills. Watch and enjoy.

Adam Wainwright might be all the way back ... or he might be better than that: The Cardinals right-hander appears to have put his 2011 surgery and his '12 rehabilitation season fully in the past. He's been absolutely brilliant in the early going, recalling his '09-10 runs at NL Cy Young Awards.

Wainwright's velocity is up, higher over his past three starts than any three-start stretch last year -- and that in the early, chilly going, before many pitchers hit their peak velocity. He's pounding the strike zone, having walked three batters all year, while allowing contact at a lower rate than in any of his previous seasons as a starter.

Wainwright is not going to walk three batters a month for the full season, of course. But there's no reason to think he can't return to the heights he scaled in 2009 and '10.

Mariano Rivera might pitch forever: OK, it's hard not to take Rivera at his word when he says he's retiring. He's one of the most respected people in the game, and not exactly known as a liar. But if you were in his shoes, still performing at a ludicrously high level, wouldn't you have to give it a second thought?

It's as though Rivera never missed a day, rather than sitting out most of 2012 due to a major knee injury. He's pitching, well, like Mariano Rivera, and that's about the best compliment you can give. Rivera is a perfect 10-for-10 on save attempts. He has yet to walk a batter this year. He's thrown a first-pitch ball to 11 out of 41 batters. He's seen four three-ball counts.

All this while doing the same thing as always: throwing that wicked cutter again and again and again. He's going to hang it up in five (or six) months, so at least be sure to enjoy it while you still can.